Congress just mandated the production of 36 billion gallons of bio-ethanol for transport fuel by 2022.
But is the current selection of bio-fuels a net good for our planet?
It's complicated, to say the least (and I'm not even getting into the economics of government mandates like that here). Excerpt:

The new studies examine a different part of biofuel equation, and both suggest that the emissions associated with the crops may be even worse than that.

One analysis looks at land that is switched to biofuel crop production. Carbon will be released when forests are felled or bush cleared, and longer-term emissions created by dead roots decaying.

This creates what Joseph Fargione of The Nature Conservancy and colleagues call a "carbon debt". Emissions savings generated by the biofuels will help pay back this debt, but in some cases this can take centuries, suggests their analysis.

If 10,000 square metres of Brazilian rainforest is cleared to make way for soya beans – which are used to make biodiesel – over 700,000 kilograms of carbon dioxide is released.

The saving generated by the resulting biodiesel will not cancel that out for around 300 years, says Fargione. In the case of peat land rainforest in Indonesia, which is being cleared to grow palm oil, the debt will take over 400 years to repay, he says.